Method of making 3D integration microelectronic assembly for integrated circuit devices

ABSTRACT

A microelectronic assembly for packaging/encapsulating IC devices, which includes a crystalline substrate handler having opposing first and second surfaces and a cavity formed into the first surface, a first IC device disposed in the cavity and a second IC device mounted to the second surface, and a plurality of interconnects formed through the crystalline substrate handler. Each of the interconnects includes a hole formed through the crystalline substrate handler from the first surface to the second surface, a compliant dielectric material disposed along the hole&#39;s sidewall, and a conductive material disposed along the compliant dielectric material and extending between the first and second surfaces. The compliant dielectric material insulates the conductive material from the sidewall. The second IC device, which can be an image sensor, is electrically coupled to the conductive materials of the plurality of interconnects. The first IC can be a processor for processing the signals from the image sensor.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/157,193, filed Jun. 9, 2011, U.S. Pat. No. 8,456,900.

FIELD OF THE INVENTION

The present invention relates to semiconductor packaging, and moreparticularly to a 3D integration package in which a semiconductor deviceis mounted on a package structure containing another semiconductordevice.

BACKGROUND OF THE INVENTION

The trend for semiconductor devices is smaller integrated circuit (IC)devices (also referred to as chips), packaged in smaller packages (whichprotect the chip while providing off chip signaling connectivity). Withrelated chip devices (e.g. an image sensor and its processor), one wayto accomplish size reduction is to form both devices as part of the sameIC chip (i.e. integrate them into a single integrated circuit device).However, that raises a whole host of complex manufacturing issues thatcan adversely affect operation, cost and yield. Another technique forcombining related chip devices is 3D IC packaging, which saves space bystacking separate chips inside a single package.

3D packaging can result in increased density and smaller form factor,better electrical performance (because of shorter interconnect lengthwhich allows for increased device speed and lower power consumption),better heterogeneous integration (i.e. integrate different functionallayers such as an image sensor and its processor), and lower cost.

However, 3D integration for microelectronics packaging faces challengesas well, such as high cost of 3D processing infrastructure andsustainable supply chain. Existing 3D IC packaging techniques to formthrough-silicon via's (TSV's), including Via-First, Via-Last andVia-middle processes, utilize semiconductor lithographic processes whichare inherently complex and costly. As a result, few companies in theworld can afford the billions of dollars in CMOS R&D per year to keeppace. Moreover, interconnects between IC packages can fail due to thestresses incurred during manufacturing and mounting, as well as thermalor vibrational stresses incurred during operation. A complementary,cost-effective TSV solution is needed to enable use of a separate butclosely coupled image processor enabling the pixel array area on theimage sensor to be maximized, and enable direct memory access, bystacking and vertically interconnecting multiple chips.

BRIEF SUMMARY OF THE INVENTION

A method of forming a microelectronic assembly includes forming a cavityin a crystalline substrate handler having opposing first and secondsurfaces, wherein the cavity is formed into the first surface thatextends toward but does not reach the second surface, placing a first ICdevice in the cavity, mounting a second IC device to the second surface,and forming a plurality of interconnects through the crystallinesubstrate handler. Each of the plurality of interconnects is formed byforming a hole through the crystalline substrate handler with a sidewallextending between the first and second surfaces, forming a compliantdielectric material along the sidewall, and forming a conductivematerial along the compliant dielectric material and extending betweenthe first and second surfaces, wherein the compliant dielectric materialinsulates the conductive material from the sidewall. The method furtherincludes electronically coupling the second IC device to the conductivematerials of the plurality of interconnects.

A method of forming a microelectronic assembly includes forming a cavityin a crystalline substrate handler having opposing first and secondsurfaces, wherein the cavity is formed into the first surface, placing afirst IC device in the cavity, mounting a second IC device to the secondsurface, and forming a plurality of interconnects through thecrystalline substrate handler. Each of the plurality of interconnects isformed by forming a hole through the crystalline substrate handler witha sidewall extending between the first and second surfaces, forming acompliant dielectric material along the sidewall, and forming aconductive material along the compliant dielectric material andextending between the first and second surfaces, wherein the compliantdielectric material insulates the conductive material from the sidewall.The method further includes electronically coupling the second IC deviceto the conductive materials of the plurality of interconnects, andforming one or more layers of insulation materials on the first surfacethat extends across an opening of the cavity in the first surface toencapsulate the first IC device in the cavity.

A method of forming a microelectronic assembly includes forming a cavityin a crystalline substrate handler having opposing first and secondsurfaces, wherein the cavity is formed into the first surface, placing afirst IC device in the cavity, mounting a second IC device to the secondsurface, and forming a plurality of interconnects through thecrystalline substrate handler. Each of the plurality of interconnects isformed by forming a hole through the crystalline substrate handler witha sidewall extending between the first and second surfaces, forming acompliant dielectric material along the sidewall, and forming aconductive material along the compliant dielectric material andextending between the first and second surfaces, wherein the compliantdielectric material insulates the conductive material from the sidewall.The method further includes electronically coupling the second IC deviceto the conductive materials of the plurality of interconnects. Thesecond IC device is an image sensor and the first IC device is aprocessor for processing signals from the image sensor. The image sensorcomprises an array of pixel sensors each including a photodetector forconverting light energy to a voltage signal, and wherein the processoris configured to receive the voltage signals and to compute orinterpolate color and brightness values for each of the voltage signalsfrom the pixel sensors.

Other objects and features of the present invention will become apparentby a review of the specification, claims and appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-10 are cross sectional side views of a semiconductor packagingstructure showing in sequence the steps in the processing of thepackaging structure in the mounting of an IC device on a semiconductorpackaging structure that houses another IC device.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is wafer level 3D IC integration package solutionthat is ideal for packaging/encapsulating IC devices, and enables 3Dintegration of multiple related IC devices such as image sensors andtheir processors. The formation of the 3D integration package isdescribed below.

The formation process begins with a crystalline substrate handler 10 asshown in FIG. 1. A non-limiting example can include a handler ofcrystalline substrate having a thickness of around 600 μm. A cavity 12is formed in the handler, as shown in FIG. 2. Cavity 12 can be formed bythe use of a laser, a plasma etching process, a sandblasting process, amechanical milling process, or any other similar method. Preferablycavity 12 is formed by photo-lithography plasma etching, which includesforming a layer of photo resist on the handler 10, patterning the photoresist layer to expose a select portion of handler 10, and thenperforming a plasma etch process (e.g. using a SF6 plasma) to remove theexposed portion of the handler 10 to form the cavity 12. Preferably, thecavity extends no further than ¾ of the crystalline substrate thickness,or at least leaves a minimum thickness at the bottom of the cavity ofaround 50 μm. The plasma etch can be anisotropic, tapered, isotropic, orcombinations thereof.

Through holes (via's) 14 are then formed through the thickness of thehandler 10 adjacent to but connecting with the cavity 12, as illustratedin FIG. 3. Holes 14 can be formed using a laser, a plasma etchingprocess, a sandblasting process, a mechanical milling process, or anysimilar method. Preferably, the through holes 14 are formed by plasmaetching in a similar manner as the formation of the cavity 12 (exceptthat the holes 14 extend all the way through the thickness of thecrystalline substrate handler 10). Plasma silicon etching (e.g.anisotropic, tapered, isotropic, or combinations thereof) allows forvarious shapes of the via profile. Preferably, the profile of holes 14is tapered, with a larger dimension at the surface through which cavity12 was formed. Preferably the minimum hole diameter is around 25 μm, andthe angles of the walls are between 5° and 35° relative to a directionperpendicular to the surfaces of the crystalline substrate through whichthe holes 14 are formed, such that the hole has a smallercross-sectional size at one surface of the crystalline substrate 10 thanthe other surface.

The through holes 14 are then filled with a compliant dielectricmaterial 16 as shown in FIG. 4, using a spin coating process, a sprayprocess, a dispense process, an electrochemical deposition process, alamination process, or any other similar method. A compliant dielectricis a relatively soft material (e.g. solder mask) that exhibitscompliance in all three orthogonal directions, and can accommodate thecoefficient of thermal expansion (CTE) mismatch between the crystallinesubstrate (˜2.6 ppm/° C.) and Cu (˜17 ppm/° C.) interconnect. Compliantdielectric material 16 is preferably a polymer, such as BCB(Benzocyclobutene), solder mask, solder resist, or BT epoxy resin.

Through holes 18 are then formed through the dielectric material 16.Holes 18 can be formed by using a CO₂ laser (e.g. spot size of about 70μm) for larger sized holes 18, or a UV laser (e.g. spot size of about 20μm at a wavelength of 355 nm) for smaller sized holes 18 (e.g. less than50 μm in diameter). Laser pulse frequencies between 10 and 50 kHz at apulse length of less than 140 ns can be used. The side walls of thethrough holes 18 are then metalized (i.e. coated with a metallizationlayer 20). The metallization process preferably starts with the desmearprocess for removing any resin smeared on the interior walls of thethrough holes 18 (caused by the drilling through dielectric materialssuch as epoxy, polyimide, cyanate ester resins, etc). The processinvolves contacting the resin smear with a mixture ofgamma-butyrolactone and water to soften the resin smear, followed bytreatment with an alkaline permanganate solution to remove the softenedresin, and treatment with an aqueous acidic neutralizer to neutralizeand remove the permanganate residues. After desmear treatment, theinitial conductive metallization layer 20 is formed by electrolesscopper plating, followed by a photo-lithography etch back so that themetallization layer extends away from the holes 18 along dielectric 16for a short distance (e.g. 25 μm or more) at both ends of holes 18 (butnot so far as to make electrical contact with crystalline substrate 10.Adhesion is obtained at the plated interface by an anchor effect fromthe surface roughness. The resulting structure is shown in FIG. 5.

A dielectric layer 22 is then formed on the surface of the handler thatdoes not contain the opening to cavity 12. Preferably, this is done byapplying a photo-imagable dielectric on the handler surface by use of aspin coating process or a spray process. A photo-lithographic process(i.e. UV exposure, selective material removal) is then used toselectively remove portions of the dielectric layer 22 over (and thusexposing) through-holes 18 and horizontal portions of metallizationlayer 20. A metal layer is then sputtered over dielectric layer 22. Aphoto-lithographic process (i.e. resist layer deposition, UV exposurethrough a mask, removal of selected portions of resist to exposeselected portions of metal layer, metal etching, and photo resistremoval) is used to selectively remove portions of the metal layerleaving metal pads 24 disposed over through holes 18 and in electricalcontact with metallization layer 20. The resulting structure is shown inFIG. 6. While not shown, the center of the metal pads 24 may have asmall hole there through aligned with through-holes 18.

An IC chip 26 is inserted into cavity 12 as shown in FIG. 7. The IC chip26 includes an integrated circuit (i.e. semiconductor device). The ICchip 26 is insulated from handler 10 by a dielectric insulating layer28. The insertion of the IC chip 26 and formation of the insulatinglayer 28 can be performed in several ways. One way is to form theinsulating layer 28 on the walls of the cavity 12 before insertion ofthe bare IC chip 26 (e.g. by spray coating epoxy, by electro-chemicaldeposition, etc.). A second way is to form the insulating layer 28 onthe back surfaces of IC chip 26 before it is inserted into cavity 12. Athird way is to form insulating layers both on the cavity walls and onthe IC chip back surfaces before chip insertion, where the twoinsulating layers are bonded together upon chip insertion to forminsulation layer 28. The IC chip 26 includes bonding pads 30 exposed onits bottom surface.

An encapsulation insulation layer 32 is then formed on the structurewhich encapsulates IC chip 26 inside cavity 12. Preferably, layer 32 isformed using a photo-imagable dielectric (e.g. a solder mask). The layeris pre-cured to partially remove solvent so the surface is not tacky. Aphoto lithography step is then performed (i.e. UV exposure throughmask), after which select portions of the insulation layer 32 areremoved to expose the IC chip bond pads 30 and the metallization layer20 extending out of the through holes 18. Post curing can then beperformed to increase the surface hardness of layer 32. A metal layer isthen deposited over insulation layer 32 (e.g. by metal sputtering,followed by the deposition of a photo-imagable resist layer). A photolithography step is then performed (i.e. UV exposure through mask andselective resist layer removal), followed by selective metal etching ofthose portions exposed by the photo resist removal, leaving metalfan-out and fan-in bond pads 34 in electrical contact with IC chip bondpads 30, and leaving interconnect bond pads 36 in electrical contactwith the metallization layer 20 extending out of through holes 18. Metalplating of the bond pads 34/36 can occur here as well. The resultingstructure is shown in FIG. 8 (after photo resist removal).

An encapsulation insulation layer 38 is then formed over insulationlayer 32 and bond pads 34/36, followed by a selective etch back toexpose bond pads 34/36. The selective etch back can be performed by aphoto-lithographic process to selectively remove those portions of layer38 over bond pads 34/36. BGA interconnects 40 are then formed on bondpads 34/36 using a screen printing process of a solder alloy, or by aball placement process, or by a plating process. BGA (Ball Grid Array)interconnects are rounded conductors for making physical and electricalcontact with counterpart conductors, usually formed by soldering orpartially melting metallic balls onto bond pads. The resulting structureis shown in FIG. 9.

An IC chip assembly 42 is then attached onto insulation layer 22, asillustrated in

FIG. 10. Attachment can be performed using conventional pick-and-placedie attachment equipment. Adhesive tape or printable/dispensable epoxymaterials can be used as the adhesive. The IC chip assembly 42 includesa second IC chip 44, and CIS bond pads 46 for signal connectivity to ICchip 44. In the exemplary embodiment of FIG. 10, IC chip 44 is an imagesensor, which includes a substrate 45, an array of pixel sensors 47 anda color filter and microlens array 48. Ideally, IC chip 26 is aprocessor for the image sensor. Au or Cu wire bonds 50 are then attachedto electrically connect each of the CIS bond pads to one of theinterconnect metal pads 24.

The IC packaging technique and the method of its manufacture describedabove and illustrated in the figures have several advantages. First, thesilicon based IC chip 26 is housed inside crystalline substrate 10,which provides mechanical and environmental protection of IC chip 26.Second, utilizing a compliant dielectric material 28 for securing ICchip 26 inside crystalline substrate 10 reduces thermal and mechanicalstresses that could adversely affect both. Third, using a crystallinesubstrate package structure with fan-out and fan-in pads for packagingIC chip 26 (which can be separately tested and verified before insertioninto packaging 10) enhances reliability and yield. Fourth, in a two chipcombination, housing one of the chips inside a crystalline substratepackage structure 10, with the other chip mounted thereon, enhancesreliability and provides a signal interconnection scheme that is fasterand more reliable. Fifth, electrical connections for both chips areprovided on a common surface of the handler 10, for efficient signalcoupling and connection. Sixth, utilizing a wafer level dielectriclamination for layer 32 provides very low impedance across a very widefrequency range. This impedance can be as much as an order of magnitudeor more lower than existing spray and spin coated dielectrics. Theseultra-thin dielectric laminates also offer the advantage of dampeningnoise on the power and ground planes and will be important for achievingacceptable electrical performance in future high speed digital designs.

There are also a number of advantages of thethrough-polymer-interconnect formed through holes 18. First, theseinterconnects are conductive elements that reliably re-route theelectrical signals from chip 44, through handler 10, to the same side ofhandler 10 which contains the electrical contacts for the IC chip 26.Second, by forming the walls of through-holes 14 with a slant, itreduces potentially damaging inducing stress on the crystallinesubstrate that can result from 90 degree corners. Third, the slantedsidewalls of holes 14 also mean there are no negative angle areas thatcan result in gaps formed with dielectric material 16. Fourth, byforming insulation material 16 first, and then forming metallizationlayer 20 thereon, metal diffusion into the crystalline substratestructure of handler 10 is avoided. Fifth, forming metal layer 20 usinga plating process is superior to other metallization techniques such assputter deposition, because the plating process is less likely to damageinsulation material 16. Sixth, using a compliant insulation material 16to form the sidewalls of holes 18 is more reliable. Seventh, thecreation of the through-polymer-interconnects using laser drillingthrough polymer, desmearing, and metal plating, is less expensive thanusing semiconductor sputtering and metal deposition tools. Finally, thewire bonding for the second IC chip 44 is disposed on the opposite sideof the package structure 10 than the bonding pads for the first IC chip26, which enables the shortest electrical path between chips andeliminates the need for a flexible and/or organic package handler forthe assembly of the image sensor.

The packaging configuration described above is ideal for and describedin the context of (but not necessarily limited to) IC chip 44 being animage sensor, and IC chip 26 being a processor for processing thesignals from the image sensor. An image sensor is a complementarymetal-oxide semiconductor (CMOS) device that includes an integratedcircuit containing an array of pixel sensors, each pixel containing aphotodetector and preferably its own active amplifier. Each pixel sensorconverts the light energy to a voltage signal. Additional circuitry onthe chip may be included to convert the voltage to digital data. Theimage processing chip comprises a combination of hardware processor(s)and software algorithms. The image processor gathers the luminance andchrominance information from the individual pixels sensors and uses itto compute/interpolate the correct color and brightness values for eachpixel. The image processor evaluates the color and brightness data of agiven pixel, compares them with the data from neighboring pixels andthen uses a demosaicing algorithm to reconstruct a full color image fromthe incomplete color samples, and produces an appropriate brightnessvalue for the pixel. The image processor also assesses the whole pictureand corrects sharpness and reduce noise of the image.

The evolution of image sensors results in the ever higher pixel count inimage sensors, and the additional camera functionality, such as autofocus, zoom, red eye elimination, face tracking, etc, which requiresmore powerful image sensor processors that can operate in higher speeds.Photographers don't want to wait for the camera's image processor tocomplete its job before they can carry on shooting—they don't even wantto notice some processing is going on inside the camera. Therefore,image processors must be optimized to cope with more data in the same oreven shorter period of time.

It is to be understood that the present invention is not limited to theembodiment(s) described above and illustrated herein, but encompassesany and all variations falling within the scope of the appended claims.For example, references to the present invention herein are not intendedto limit the scope of any claim or claim term, but instead merely makereference to one or more features that may be covered by one or more ofthe claims. Materials, processes and numerical examples described aboveare exemplary only, and should not be deemed to limit the claims.Further, as is apparent from the claims and specification, not allmethod steps need be performed in the exact order illustrated orclaimed, but rather in any order separately or simultaneously thatallows the proper formation of the IC packaging of the presentinvention. Single layers of material could be formed as multiple layersof such or similar materials, and vice versa. While the inventivepackaging configuration is disclosed in the context of IC chip 26 beingan image sensor processor and IC chip 44 being an image sensor, thepresent invention is not necessary limited to those IC chips.

It should be noted that, as used herein, the terms “over” and “on” bothinclusively include “directly on” (no intermediate materials, elementsor space disposed therebetween) and “indirectly on” (intermediatematerials, elements or space disposed therebetween). Likewise, the term“adjacent” includes “directly adjacent” (no intermediate materials,elements or space disposed therebetween) and “indirectly adjacent”(intermediate materials, elements or space disposed there between),“mounted to” includes “directly mounted to” (no intermediate materials,elements or space disposed there between) and “indirectly mounted to”(intermediate materials, elements or spaced disposed there between), and“electrically coupled” includes “directly electrically coupled to” (nointermediate materials or elements there between that electricallyconnect the elements together) and “indirectly electrically coupled to”(intermediate materials or elements there between that electricallyconnect the elements together). For example, forming an element “over asubstrate” can include forming the element directly on the substratewith no intermediate materials/elements therebetween, as well as formingthe element indirectly on the substrate with one or more intermediatematerials/elements therebetween.

What is claimed is:
 1. A method of forming a microelectronic assembly,comprising: forming a cavity in a crystalline substrate handler havingopposing first and second surfaces, wherein the cavity is formed intothe first surface that extends toward but does not reach the secondsurface; placing a first IC device in the cavity, wherein the first ICdevice has a bottom surface with conductive pads facing away from thesecond surface; mounting a second IC device to the second surface;forming a plurality of interconnects through the crystalline substratehandler, wherein each of the plurality of interconnects is formed by:forming a hole through the crystalline substrate handler with a sidewallextending between the first and second surfaces, forming a compliantdielectric material along the sidewall, forming a conductive materialalong the compliant dielectric material and extending between the firstand second surfaces, wherein the compliant dielectric material insulatesthe conductive material from the sidewall; electronically coupling thesecond IC device to the conductive materials of the plurality ofinterconnects; forming electrical interconnects over the first surfaceof the handler with each electrically coupled to the conductive materialof at least one of the plurality of interconnects; and formingelectrical interconnects over the bottom surface of the first IC devicewith each electrically coupled to at least one of the conductive pads ofthe first IC device.
 2. The method of claim 1, wherein the compliantdielectric material includes a polymer.
 3. The method of claim 1,wherein for each of the plurality of interconnects, the hole is taperedsuch that the hole has a smaller cross-sectional dimension at the secondsurface than at the first surface.
 4. The method of claim 1, wherein foreach of the plurality of interconnects, the sidewall extends in adirection between 5° and 35° relative to a direction that isperpendicular to the first and second surfaces.
 5. The method of claim1, wherein the formation of each of the plurality of interconnectsfurther comprises: forming a first bond pad over the hole at the firstsurface and electrically coupled to the conductive material; and forminga second bond pad over the hole at the second surface and electricallycoupled to the conductive material.
 6. The method of claim 5, whereinelectrically coupling the second IC device to the conductive materialsof the plurality of interconnects includes electrically coupling aplurality of wires between the second IC device and the second bondpads.
 7. The method of claim 1, wherein the second IC device is an imagesensor and the first IC device is a processor for processing signalsfrom the image sensor.
 8. A method of forming a microelectronicassembly, comprising: forming a cavity in a crystalline substratehandler having opposing first and second surfaces, wherein the cavity isformed into the first surface; placing a first IC device in the cavity,wherein the first IC device has a bottom surface with conductive padsfacing away from the second surface; mounting a second IC device to thesecond surface; forming a plurality of interconnects through thecrystalline substrate handler, wherein each of the plurality ofinterconnects is formed by: forming a hole through the crystallinesubstrate handler with a sidewall extending between the first and secondsurfaces, forming a compliant dielectric material along the sidewall,forming a conductive material along the compliant dielectric materialand extending between the first and second surfaces, wherein thecompliant dielectric material insulates the conductive material from thesidewall; electronically coupling the second IC device to the conductivematerials of the plurality of interconnects; forming one or more layersof insulation materials on the first surface that extends across anopening of the cavity in the first surface to encapsulate the first ICdevice in the cavity; forming electrical interconnects over the firstsurface of the handler with each electrically coupled to the conductivematerial of at least one of the plurality of interconnects; and formingelectrical interconnects over the bottom surface of the first IC devicewith each electrically coupled through the one or more layers ofinsulation materials and to at least one of the conductive pads of thefirst IC device.
 9. The method of claim 8, wherein the forming of theelectrical interconnects over the bottom surface of the first IC devicecomprises: forming a plurality of bond pads that are electricallycoupled to the first IC device and extend a least partially through theone or more layers of insulation materials.
 10. The method of claim 9,wherein the forming of the electrical interconnects over the bottomsurface of the first IC device comprises further comprises: forming aplurality of rounded interconnects each electrically connected to one ofthe plurality bond pads.
 11. A method of forming a microelectronicassembly, comprising: forming a cavity in a crystalline substratehandler having opposing first and second surfaces, wherein the cavity isformed into the first surface; placing a first IC device in the cavity,wherein the first IC device has a bottom surface with conductive padsfacing away from the second surface; mounting a second IC device to thesecond surface; forming a plurality of interconnects through thecrystalline substrate handler, wherein each of the plurality ofinterconnects is formed by: forming a hole through the crystallinesubstrate handler with a sidewall extending between the first and secondsurfaces, forming a compliant dielectric material along the sidewall,forming a conductive material along the compliant dielectric materialand extending between the first and second surfaces, wherein thecompliant dielectric material insulates the conductive material from thesidewall; electronically coupling the second IC device to the conductivematerials of the plurality of interconnects; forming electricalinterconnects over the first surface of the handler with eachelectrically coupled to the conductive material of at least one of theplurality of interconnects; and forming electrical interconnects overthe bottom surface of the first IC device with each electrically coupledto at least one of the conductive pads of the IC device; wherein thesecond IC device is an image sensor and the first IC device is aprocessor for processing signals from the image sensor; wherein theimage sensor comprises an array of pixel sensors each including aphotodetector for converting light energy to a voltage signal, andwherein the processor is configured to receive the voltage signals andto compute or interpolate color and brightness values for each of thevoltage signals from the pixel sensors.